Oceans of Energy

by Gretchen Noyes-Hull

Limpets and Sea Snakes, Nodding Ducks and Ospreys, Mighty Whales and Wave Dragons! These are not, as you might think, the names of twisting and twirling carnival rides. They are the fanciful descriptions given to some very serious inventions. Scientists around the world, intent on harnessing the power of the oceans, are building and testing a variety of futuristically shaped designs.

It comes as no surprise that we are looking to the oceans of the world for a reliable source of energy for the future. Their surface waters collect and store massive amounts of thermal (heat) energy from the sun. Some of the heat fuels the winds that blow across the expanses of ocean, building higher and higher waves. Anyone who visits the beach is “moved” by the enormous kinetic energy of the waves. But did you know that the waves are powered by the sun?

Even on cloudy days, the oceans are busy storing energy. The gravity of the moon and the sun tugs at the ocean waters, causing the tides to rise and fall each day as the Earth turns on its axis. Like a battery, the ocean stores potential energy, the energy resulting from the difference between high and low tide.

Heat, waves, tides—there is more than enough energy in the oceans to meet all our needs! Free for the taking, and totally “renewable”! How easy will it be for us to coax the oceans to share it with us here on land? How much of our future energy will come from the sea? Scientists and engineers are putting their heads and imaginations together to find the answers.

Tide of Events

It's not the first attempt. A patent was drawn up in 1799 for an invention to harness the waves to run machinery. And tides were used to turn water wheels for many mills more than a century ago. But times have changed. Our world runs on electricity now. The energy of the ocean must be put to work spinning the turbines and coils of electrical generators to provide that electricity.

Tidal dams built across estuaries seemed a very promising solution to the growing energy “crunch.” Water rushing through tunnels in the dams spins built-in turbines and generators on the incoming tide while raising the water level behind the dam. After the tide turns, outgoing water again turns the turbines, the other way this time. Tidal turbines have produced a very significant amount of ocean electricity at the La Rance Dam in France since they first turned in 1966.

But the “tides have turned” against the use of dams. Because the time of the high and low tides changes every day, the peak time in electricity production also changes. And the tides don't always coincide with the time that lights are switched on or when favorite TV programs are scheduled. Since dams also can damage estuaries and the creatures that inhabit them, a better solution was needed. A search for it has begun.

Turning On the Lights

This year, the world's “most northern town,” at the Arctic tip of Norway, became the very first one to receive electricity from an underwater tidal turbine. Looking very much like large wind turbines on land, the blades of these submerged structures turn so slowly that fish don't even notice them or the thick cables that bring the electricity ashore. The tidal turbines are a welcome addition to the town of Kvalsund, Norway. Solar power is not an option in this place, where for two months of the year the sun never rises!

The independence-minded people of the community of Islay, Scotland, also enjoy reading by “the light of the ocean.” Their electricity comes not from the tides but from the waves pounding on the shore of their small island. Built into the rocks is the aptly named “Limpet” generating station. (A limpet is a one-shelled mollusk that tightly holds itself to the rocks in the zone between high and low tide.) The waves flowing into the Limpet squeeze a column of air that turns a turbine to generate electricity. When they are not reading, the residents of Islay may survey their island from a “wave-powered bus.”

Ups and Downs…

Waves are powerful, and they can be destructive. The same pounding surf that turns on the lights in Islay shakes and hammers any structure anchored on or near shore. And it is pretty hard to even build a generating station when the surf is breaking over your head! (Several designs have been destroyed by the waves before they were even completed.)

A “menagerie” of new devices is now being tested that trap the energy of the more gentle offshore waves. Competitors are racing to come up with the best design for surfing and grabbing the energy of the more predictable broad offshore swells.

This year the “Pelamis” sea snake is being tested off the coast of Northern Scotland. Four huge steel buoys rise and fall with the passing of each ocean swell. The flexing of the joints that connect the buoys captures the energy and converts it to electricity that is “wired” to shore. So far, the snakes seem to be ahead of the “clams,” “ducks,” “mighty whales,” and other members of the floating wave zoo in electricity production. The stakes are high: It is predicted that wave devices may someday provide 10 percent of the world's electricity. Although the price tag for installation is steep, the cost afterward is low. The waves will continue to roll as long as the sun shines.

And where the sun shines the warmest, in the tropics, heat energy can be extracted directly from the ocean. The oceans are often tagged the “biggest solar collector,” but all that energy is stored only in the upper layers of water. Deep down, the oceans are as cold at the equator as they are at the poles! When the difference in temperature between the top and the bottom is big enough (about 68 degrees F), it can be used to produce electricity. Around the world today, investigators are encouraging the upper layers of the oceans to give up their heat energy through a process called “thermal conversion.” (When the warm water is caused to boil and turn to steam under low pressure, the steam is used to turn a turbine for electricity production. Then the deep cold water is used to change the steam back to water again.)

Wave or tidal, tropical or polar, onshore or offshore, oceans of energy cover over 70 percent of our planet. Developing ways to harness that energy is limited only by our imagination. In the not-so-distant future you might be reading another article by “ocean light,” powered by limpets, sea snakes, and dragons!

Vocabulary

estuary:

The part of the wide lower course of a river where its current is met by ocean tides.

kinetic energy:

The energy possessed by a body because of its motion, equal to one-half the body's mass times the square of its speed.

potential energy:

The energy of a particle or system of particles derived from position or condition, rather than motion. A raised weight or charged battery has potential energy.

Activity

Is the energy collected by wave turbines kinetic or potential energy? Why? What would be another way to describe the energy collected? Answer: The energy collected by wave turbines is kinetic energy because it is energy that comes from a moving object. The energy collected from waves and tides is mechanical energy.

Once the energy is collected by the wave turbines and stored in a battery, is it kinetic or potential energy? What would be another way to describe the energy stored?Answer: When the energy has been collected and stored in a battery, it becomes potential energy. The energy in the battery exists as chemical energy.

Design a simple machine that would turn the energy from tides into sound energy. Include a diagram to show how the tide energy is collected and how it is changed into sound energy. What must be done to the tide energy to transform it? Write a few sentences to explain how your machine works.Answer: Answers will vary.

Activity

Is the energy collected by wave turbines kinetic or potential energy? Why? What would be another way to describe the energy collected? Answer: The energy collected by wave turbines is kinetic energy because it is energy that comes from a moving object. The energy collected from waves and tides is mechanical energy.

Once the energy is collected by the wave turbines and stored in a battery, is it kinetic or potential energy? What would be another way to describe the energy stored?Answer: When the energy has been collected and stored in a battery, it becomes potential energy. The energy in the battery exists as chemical energy.

Design a simple machine that would turn the energy from tides into sound energy. Include a diagram to show how the tide energy is collected and how it is changed into sound energy. What must be done to the tide energy to transform it? Write a few sentences to explain how your machine works.Answer: Answers will vary.